1. Field of the Invention
The present invention generally relates to a wheeled vehicle with an arm unit, and more particularly relates to a wheeled vehicle having an arm unit that carries a wheel of the vehicle.
2. Description of Related Art
Wheeled vehicles such as, for example, motorcycles have a plurality of wheels rotatably coupled with a body frame. Typically, motorcycles have front and rear wheels. A prime mover such as, for example, an engine powers the rear wheel. The front wheel usually is steerable by the rider.
In a typical motorcycle, a rear portion of the body frame has a generally horizontal pivot shaft that extends in a transverse direction. The pivot shaft supports a rear arm unit (or swing arm) for pivotal movement about a pivot axis defined the pivot shaft. That is, the rear arm unit can swing up and down about the pivot axis. The rear arm unit carries the rear wheel. The arm unit generally includes a pair of support sections through which the pivot shaft extends, a pair of arm sections that extend from the respective support sections to carry the rear wheel, and a connecting section that connects the respective arm sections with each other.
Recently, hydroforming has become practicable for producing motorcycle components. The components produced by hydroforming can be thinner and lighter than those produced by casting or other production processes. The arm unit, of course, can benefit from these advantages. Conventionally, however, a portion of the arm unit that needs to have increased rigidity is still produced by casting while the other portions can be produced by hydroforming. For example, JP2003-2274A discloses such an arm unit. Each arm section of the arm unit in this publication has a coupling portion with which the connecting section coupled. The coupling portions are produced by casting because the coupling portions require increased rigidity.